The present invention relates to a polyurethane-forming system for the production of reinforced polyurethane composites by a vacuum infusion process and to the composites produced from this system. The processing characteristics of this system and the physical properties of the composites produced from this system of the present invention are particularly advantageous for producing large articles. The composites of the present invention are particularly suitable for applications such as turbine wind blades.
Reinforced composites are being used for a number of applications where strength and light weight are important physical properties. Examples of applications for which reinforced composites are employed include automotive components and construction materials.
To date, the applications for which fiber reinforced composites have been used have been limited by the processability of the polymer-forming system and the properties of the polymeric material used to produce the composite. More specifically, production of larger composite articles requires a liquid reactive system having a viscosity that is low enough to thoroughly penetrate the reinforcing material and a reactivity slow enough that it will not set completely before the form or mold has been completely filled but not so slow that production of a single molded composite article will require such an extremely long period of time that it becomes uneconomical to produce a composite article with that material.
One method for increasing the speed with which a reactive system is introduced into the reinforcing material is a vacuum infusion molding process. In a vacuum infusion molding process, the reinforcing material is positioned within a vacuum chamber. The pressure within this vacuum chamber is then drawn down. The pressure differential, between the bag in which the pressure has been reduced and the atmospheric pressure on the reactive mixture to be fed into the bag pushes the reactive mixture into the bag and into the reinforcing material. This technique is not, however, without its problems. Localized areas of the composite produced may exhibit less than optimum physical properties due to poor fiber volume control, lower fiber volume and excess resin.
Attempts to resolve the problems encountered with the vacuum infusion process have included the use of a specially designed mold (U.S. 2008/0237909), use of a double vacuum chamber resin infusion device (U.S. 2008/0220112), use of multiple flow injection points, introduction of a thermoplastic material in two separate stages (U.S. 2010/0062238), and production of smaller segments of the desired, article with subsequent joinder of those segments (U.S. 2007/0183888).
However, these techniques require specially designed equipment and/or multiple process steps.
To date, modification of the polymer-forming reaction mixture, especially a polyurethane-forming reaction mixture has not been an approach that has been successfully implemented in a vacuum infusion process for producing large composite articles such as wind turbines.
It would, therefore, be advantageous to develop a polyurethane-forming system having a viscosity that is sufficiently low that it can be successfully infused into a reinforcing material before the polyurethane-forming reaction has been completed and a reactivity that is not so slow that production of the composite becomes economically impractical.